The invention relates to the field of video image processing, and in particular to the field of determining motion vectors that are each coordinated with individual regions in an image.
In image processing, it is known in the art to coordinate individual regions of an image in a sequence of images with motion vectors, each of which indicates a shifting in the position of an image region relative to a position of this same region in a preceding or succeeding image of the sequence. The motion information obtained in this way is useful, for example, in generating one or more intermediate images lying in time between the images of the sequence, to correctly represent the position of moving objects in the intermediate images, i.e., in a manner oriented to the motion. The motion information of an object or image region moving through several consecutive images can also be used for a compressed storage of image data of consecutive images.
One of several possible methods for generating such motion vectors is the block matching method, which is described, for example, in Blume, H., Nonlinear error-tolerant interpolation of intermediate images, Fortschrittberichte VDI, 1997, Chapter 5.1.3, pages 57-60. In this method, the current image of a sequence is divided into a number of blocks of equal size. For each of these blocks, a search is conducted in the preceding or following image for the block whose contents have the best match with the content of the particular block of the current image. The displacement vector between this block of the current image and the block of the preceding or following image having the best match with this block of the current image then forms the motion vector for this block of the current image.
In the full search algorithm, each block of the current image is compared to each block of the preceding or following image to determine the motion vectors of the individual regions. To reduce the considerable computational expense required in the full search algorithm, predictive estimating procedures are known, in which motion information from previous motion estimates is taken into account when determining the motion vector for a block.
The quality of the motion estimate with the block estimation method depends heavily on the block resolution, i.e., the size of the individual blocks. The quality is greater as the individual blocks are smaller, and thus as the resolution of the image into individual blocks is better and as more motion vectors are determined per image. On the other hand, the computational expense also increases as the block size becomes smaller. Also the error likelihood for wrong estimates is greater as the block sizes become smaller. Thus, it is believed that a useable block size is approximately 4 lines by 8 pixels. This size yields clearly distinguishable block structures during the image processing.
To enhance the resolution for determination of motion vectors, U.S. Pat. No. 5,148,269 teaches how to divide the image into a predetermined number of main blocks and perform a first block estimation, to coordinate each of these main blocks with a motion vector. Each individual main block is then divided into a number of subblocks, and each subblock is coordinated with a motion vector. To generate the motion vectors of the subblocks, the motion vector of the particular main block and the motion vectors of the other main blocks which adjoin the main block are utilized.
What is needed is a method and device for determination of motion vectors offering an enhanced resolution for a justifiable additional computational expense.